Lithographic printing uses a planographic printing plate, that is, a plate in which the printing and non-printing areas are in the same plane rather than being vertically displaced from each other. The printing areas are distinguished from the non-printing areas by being hydrophobic, whereas the printing areas are hydrophilic. In operation, a lithographic printing plate is covered with a thin film of a so-called "fountain solution" (sometimes also called etch, water, or dampener) which enables the printing plate to be properly inked. The fountain solution is mostly or even entirely water and adheres to the hydrophilic areas of the plate. When the plate is thereafter subjected to inking by means of an oily, ink-covered inking roller, those areas of the plate that are hydrophobic pick up ink and can be used for printing whereas those areas that are hydrophilic refuse ink and do not print.
With commercial lithographic presses that make many impressions it has been found that various additives to the fountain solution increase the quality of printing and the number of impressions that can be made with a given set of printing plates. Common fountain solution additives include gum arabic and various other water soluble polar polymers that act to maintain a uniform film of water over the hydrophilic areas of the printing plate. Other additives control Ph, lower surface tension, prevent foaming, prevent bacterial or fungal growth, prevent corrosion, or maintain a hydrophilic oxide in the non-printing areas. Much art exists in the details of fountain solution composition for the various printing tasks, and many specialists exist in the field.
It is known that the addition of ethyl or isopropyl alcohol to a given fountain solution in the amount of about 10 to 50% by volume (of the amount of water) increases the quality of printing. The improvement obtains over almost all types of lithographic printing (small office units, intermediate sized sheet fed units, and massive publication devices). To my knowledge the reason for the effectiveness of such alcohols has never been fully understood. It is known that one effect of alcohol, namely the lowering of surface tension, is important; however, the use of various surfactants that lower surface tension to the same levels as ethyl or isopropyl alcohol do, are, for some reason, not as effective as the alcohols themselves.
Though practice is far from uniform over the printing industry, fountain solution additives other than alcohol are usually sold as concentrates and are called etch or fountain solution concentrates. The fountain solution is made by diluting the etch concentrate with water. The alcohols or their substitutes are usually added after the fountain solution is made and are called additives. I shall follow these conventions in the material presented below. In particular I use the terms "fountain solution" and "etch" to mean that entity which is achieved by diluting an etch or fountain solution concentrate with water. "Fountain solution concentrate" is used to mean concentrates for fountain solutions which contain gum, buffers, oxidants, surfactants, biocides and so forth, but not containing alcohol or alcohol substitutes.
The use of isopropyl and ethyl alcohol is widespread in the printing industry, and such use causes some definite problems. Though isopropyl and ethyl alcohols are inexpensive, the massive amounts used in a high volume printing plant add considerably to the cost of printing. Both isopropyl and ethyl alcohol are flammable and both are toxic and irritating. Moreover, their use represents a heavy environmental load. As a result many printers have either prohibited their use or are attempting to at least cut back on the amount used. At the present time many printers maintain that the curtailment of alcohol causes a decrease in quality and greater difficulty associated with the running of a printing plant.